Protein-losing Enteropathies

When concerned with protein loss of any cause, one should measure serum albumin concentrations as opposed to the serum total protein concentration. Do not use human clinical pathology laboratories because their technology sometimes does not detect canine albumin; this means that they routinely report serum albumin concentrations of < 1.5 gm/dl in clinically normal dogs. If the patient has substantial hypoalbuminemia, the first step is to examine the skin for obvious lesions which can cause protein loss. Cutaneous lesions sufficient cause such hypoalbuminemia are obvious; you should be able to just look at the patient and know if this is the problem or not. Next, hepatic function testing (e.g., resting and post-prandial serum bile acid concentrations) and a urinalysis are requested. If there is any doubt on the urinalysis, then a urine protein:creatinine ratio will quantify the magnitude of urinary protein loss. Severe hypoalbuminemia (i.e., < 2 gm/dl) in an animal with diarrhea suggests a protein-losing enteropathy (PLE); however, diarrhea (even when severe) in no way is sufficient to eliminate hepatic disease as the cause of the hypoalbuminemia. Furthermore, a very substantial number of dogs and cats with PLE do not have vomiting or diarrhea. Some only have ascites, and some are found fortuitously on routine blood work. This may be especially true of dogs with primary intestinal lymphangiectasia.

In general, once severe, exudative cutaneous disease, protein-losing nephropathy, and hepatic insufficiency are eliminated, then PLE is a reasonable tentative diagnosis of exclusion in patients with a serum albumin < 2.0 gm/dl. Fecal concentrations of alpha-1 protease inhibitor can be used as a means of confirming PLE if there is confusion because of concurrent hepatic or renal disease. The major use for this test in clinical medicine seems to be the hypoalbuminemic patient in which you strongly suspect PLE (e.g., based upon it having severe diarrhea or having hypocholesterolemia), but which also has PLN and/or hepatic disease. However, there are several nuances about this test, especially collecting samples, that make it potentially difficult to interpret. We seldom need this test in clinical practice. Finally, contrary to what the textbooks say, PLE may be associated with a low, normal or increased serum globulin concentration. […]